The present invention relates to ground based satellite control and, more particularly, to a system which utilizes multiple ground stations to sense an undesirable state change on a satellite and automatically transmit the command sequence required to place the satellite into a desired state.
Operational satellites require two-way communications in order to function. Satellite telemetry data is transmitted from in-orbit satellites to a ground station in order to indicate the state of specific satellite operational parameters. Satellite command data is transmitted to in-orbit satellites in order to deliberately execute a change in specific satellite operational parameters. The ground-control system consists of a coordinated network of multiple ground-control sites, each site containing the necessary personnel, computers, baseband and radio frequency (RF) equipment to receive/process satellite telemetry, and generate/transmit commands to multiple satellites.
Often, a change in telemetry indicates a change in the state of specific satellite parameter(s). This occurs constantly in the normal course of satellite operations. Occasionally, a state change occurs that is considered undesired because it will cause a customer service outage and/or potential damage to the satellite. Undesired state changes usually require responses from the ground-control system. A ground station to satellite response consists of recognition by the ground-control system of a true undesired state change, and then transmitting the required commands to the satellite to place the parameter into a desired state. An expedient response minimizes the effects of an undesired state change.
Traditionally, responses have involved human interaction which has limited the speed of the response. Ground-loop control techniques have been documented solely for the attitude controlling aspects of autonomous satellite ground-control; this requires an extensive implementation and dedicated ground-control equipment (see Ground Loop Attitude Control System (GLACS) by Telesat Canada and U.S. Pat. No. 5,992,799 to Gamble et al.).
Other efforts to address these issues included the deployment of redundant ground commanding, monitoring, and control sites in geographically separated locations and the use of customized software to synchronize commanding activities between these sites. Activities at the redundant backup site can compromise an automated response without customized software designed to handle very specific undesired state-change events for very specific satellite architectures. Such software requires specialized testing and extensive empirical validation. System maintenance becomes prohibitively labor intensive requiring extensive software modifications as the legacy software system evolves to handle an ever-expanding ground system requirement set as a satellite fleet expands with time.
In addition, the customized solution described above assumes that a current primary/backup relationship between two sites will remain unchanged indefinitely. This puts unreasonable constraints on the allocation and availability of ground system resources. Customized software solutions solve undesirable telemetry state change issues in a very specialized fashion. A customized approach proves to be inappropriate and ineffective as the number and types of telemetry states that can benefit from a n automated command response system grows appreciably as a satellite fleet expands and diversifies.
This type of operational environment makes it imperative to deploy a more flexible and generic solution that would serve to resolve such problems for any set of telemetry states that needed to be automatically monitored for an entire fleet of satellites operating concurrently.
Finally, customized software solutions in the past have failed to account for automatic commanding events scheduled and stored on-board a satellite. For those satellites currently in orbit that have scheduled automatic commands stored in onboard command registers, uncontrolled automatic commanding from a ground station would conflict with those on the affected satellite and could prove deleterious to the health and/or performance of the satellite.
In an exemplary embodiment of the invention, a ground-control system provides a highly reliable means that automatically recognizes undesirable telemetry state changes and automatically transmits the required commands to the proper satellite to place the satellite operational parameters into the desired state.
According to the invention, there is provided a ground-control system that utilizes inter-site communications links, hardware, software and two redundant ground-control sites with any of the other available ground-control sites in the system acting as hot stand-by sites. The invention comprises a primary (control) site and a back-up (monitor) site, both of which constantly and independently monitor and verify validity of satellite telemetry. Upon occurrence of an undesired state change (event) upon a particular satellite, ground-control computers at both sites independently recognize the event and automatically begin a response. The control site computer verifies no critical satellite on-board commanding is scheduled to take place, discontinues interruptible activities, the monitor site computer stops any transmission to the event satellite, the control site switches the RF hardware to access the proper satellite and transmits the required commands.
If the control site computer cannot interrupt activities, it directs the monitor site computer to verify no critical satellite on-board commanding is scheduled to take place and then discontinues interruptible activities to transmit the required commands. If the monitor site computer cannot interrupt activities, it passes the response back to the control site where the control site stores the required commands in the queue until activities can be interrupted for their transmission.
The sharing of commanding computer equipment between multiple satellites at a given ground-control site minimizes the efforts and resources associated with purchasing, updating and maintaining the equipment and associated hardware.
The preferred embodiment uses dual ground-control sites which utilize the redundancies associated with this dual path arrangement and maximizes the likelihood of a successful response. Using two independent and geographically diverse sites has the benefit of minimizing the possibility of ground command transmission problems that are associated with weather and natural disasters; there is a low likelihood that both sites will be affected simultaneously.
In accordance with the invention, the preferred embodiment provides a ground system software/hardware architecture which is robust enough to provide the following features:
geographically distributed multiple site spacecraft fleet command system architecture;
multiple site dynamically configurable control/monitor redundant ground site configuration setup via database specifications and/or real-time graphics user interface (GUI) supported system software directives;
compatibility with any commercially available geosynchronous spacecraft;
hierarchical rules-based design to accommodate sequential back- to-back event handling;
flexible database driven design that supports/anticipates a wide range of dynamically configurable operational requirements and contingencies without modifications to the ground-control system software;
system support for both saved and default ground-control system application server initialization/reconfiguration;
graceful accommodation and synchronization of dynamically changing database system parameters in a distributed environment (i.e., a controlled-distribution approach to update and maintain system""s main database files); and
distributed tracking mechanism to aid in the arbitration between ground-system commanding events and on-board spacecraft automatic commanding events.